| Based on field investigation and indoor analysis of samples,this paper studies the biomass and cycling characteristics of 13 nutrients in all layers of the plantation ecosystem of Larix principis-rupprechtii,a kind of fast-growing and high-yielding timber tree which is located in Ji County in loess hilly region of west Shanxi Province.The characteristics and distribution of biomass,the characteristics and distribution of nutrient elements,and the nutrient cycling in four sub-chambers of the Larix principis-rupprechtii plantation ecosystem were estimated.Results show that the diameter class(the density distribution was like an inverted "V")and the tree height of of Larix principis-rupprechtii plantation ecosystem is related to the biomass in the form of a power function,and the w=a(D2H)b model fits better.The accumulation of biomass in the arborous layer is mainly in the trunk,which is a typical fast-growing and high-yield timber tree.The main roots are distributed in soil at a depth between 0-40cm,and there is only a very small proportion of reservation roots and absorption roots in soil below a depth of 40cm.As the roots are mainly distributed at the surface,its development would be restricted by the soil thickness if the main root was not strong enough.The crown closure is suiTab.on both the Yin and Yan slopes in the hilly and gully regions of Shanxi and Shaanxi provinces,and appropriate thinning can be carried out.When there is a complete canopy,cleaning cutting can be carried out.As the biomass in branches is slightly low,all living branches should be retained during pruning activities.The biomass level in the shrub layer is 1.62lt/hm2,much lower than that of the same species in natural forest.The litterfall layer is thick,with a natural water content of 75.3%,a maximum water holding capacity of 298.1%,and a normal water storage capacity.The arborous layer,the shrub layer and the grass layer can be ranked in an ascending order according to the content of the nutrition elements in the Larix principis-rupprechtii plantation ecosystem.The contents of Zn,Fe and Mn are high in all layers,and the harmful metals such as Cr,Cu,Ni and Cd are low and less than 0.04 Mg·g-1.According to Ducan significant difference analysis of many groups of samples,there is no obvious difference in the content of N and Ni in roots,shrubs and barks,the content of P in barks,fruits and roots,the content of K in barks,trunks,fruits and shrubs,the content of Ca and Cr in branches and shrubs,the content of Mg,Na in fruits,roots,and barks,the content of Fe and Mn in trunks,branches and barks,the content of Cu in in branches,fruits and herbs,the content of Cd in leaves and branches,and the content of Zn in leaves and fruits(p>0.05).The content of Mg in soil is not affected by depth,and the content of N decreases with the increase of depth with a sTab.change,which is highest in the surface.The content of P decreased rapidly in soil with a depth between 10cm and 40cm.The content of Fe is much higher than other trace elements,which is about 20 times the content of Zn.The content of trace elements is vertically distributed in the soil layer,which all decrease except Zn,indicating that these elements are leached downward in the soil.There is significant difference in the content of N except in soil between a depth of 60-80cm and 80-100cm and the content of P except in soil between a depth of 20-40cm and 80-100cm(p<0.05).The content of P,Zn and Cu in litterfall layer decreases greatly due to the leaching.The nutrient contents are similar in leaves and litterfall leaves.The total amount of fallen branches and barks accounts for less than 40%of the total litterfall.The nutrient content in rainfall outside the forest in the study area iss lower than that in rainfall through forest canopy,and all large-amount nutrient elements and the Cu and Mn contents in the runoff water are higher than those in rainfall outside the forest and rainfall through forest canopy.with P as the biggest change(followed by K and Ca),which are 56 and 7 times higher than that in rainfall outside the forest and rainfall through forest canopy separately.The content of P in rainfall outside the forest and rainfall through forest canopy are low,which comes mostly from the atmospheric dust and is difficult to be leached.Cycling symbol of thirteen nutrient elements in ecosystem of 23-year-old plantation of Larix principis-rupprechtii in Jixian County,Shanxi Province is studied through survey of sample plots and indoor sample analysis.Spatial distribution of biomass in different organs of plantation ecosystem in the study area is measured,with accumulation and distribution of nutrient elements in spatial variation combined with organ nutrient content of trees obtained;nutrient content and nutrient accumulation&distribution of other chambers of the four major chambers(forest,soil,litter and atmosphere)are measured to obtain annual nutrient return of Larix principis-rupprechtii plantation in nutrient cycling of 134.719 kg hm-1·a-1,annual storage of 53.409 kg hm-2·a-1 and annual absorption capacity of 188.129 kg·hm·2·a-1;at last,in summary of nutrient cycling in above cambers,parameters and indicators reflecting characteristics of nutrient biological cycle of the forest ecosystem are obtained.Average cycle coefficient of N,P,K in plantation ecosystem of Larix principis-rupprechtii in the study area is 0.68,revealing that cycling of ecosystem in the study area is faster;utilization coefficient is small,storage efficiency is slow and soil nutrient use efficiency is higher;nutrient elements that passed through canopy is significantly increased(canopy interception of 142.1mm),with normal requirement on precipitation(587.8mm).Higher enrichment factor enables it to adapt to barren environment with low nutrient consumption.As a whole,Larix principis-rupprechtii is of great potential for forest regeneration and afforestation. |
PDF Full Text Request